DENSIFICATION AND GRAIN-GROWTH OF IRON ULTRAFINE POWDER DURING PRESSURE-SINTERING

A green compact was pressure sintered under 100 and 200 MPa at 673-973 K for 1. 8 ks in flowing hydrogen. The nearly full densification temperatures under 100 and 200 MPa were lower by about 150 K and above 300 K respectively than that (970 K) in pressureless sintering. The minimum value of the average grain size in the dense pressure sintered compact was about 0. 15 mu m which was smaller than 1. 2 mu m of the pressureless sintered compact. The hardness of the pressure-sintered compact was as high as about 385 H//v compared with about 85 H//v of the coarse grained metal. The Hall-Petch linear relationship between H//v and the square root of the grain size was confirmed to hold also for the grain size range larger than about 0. 15 mu m.